1. Field of the Invention
The present invention relates to an image recording method and an image recording apparatus for recording images by using the image recording method.
2. Description of the Related Art
Image recording apparatus such as page printers are provided with a frame memory of a storage capacity capable of storing image data corresponding to a one-page portion, and record one page of an image at a time after temporarily storing in the frame memory image data inputted through a scanner or the like or image data transferred thereto from a host computer or the like. In recent years, there has been a demand for image recording apparatus such as page printers capable of recording high-quality images, and in the case of electrophotographic-type laser beam printers, for instance, printers capable of recording images with a high resolution of 400 dpi (dots per inch) or thereabouts are becoming a mainstay. In addition, there has been a growing demand for printers capable of recording color images and images having a large number of gradations (colors), and color page printers of a relatively small number of colors adopting a fusion-type heat transfer system have become available. Thus, there has been a demand for image recording apparatus capable of recording images with high image quality, i.e., with a high resolution and a large number of gradations.
However, in order to realize a page printer for recording images having a large number of gradations (colors) and a higher resolution, as in the case of silver halide photography or a sublimation-type heat transfer method, it is necessary to record images by using image data having a large number of gradations and a high resolution, so that the amount of image data becomes huge. As a result, it is necessary to mount on a printer body a large-capacity frame memory capable of storing the huge amount of image data, which entails the problem that the cost of the page printer becomes high. For instance, in order to store image data having full colors (16,770,000 colors) in terms of the number of gradations and a resolution of 400 dpi, the number of pixels required is 4583.times.3215 and the number of bits per pixel required is 24 (8 bits for cyan (C), magenta (M), and yellow (Y), respectively), so that a frame memory having a storage capacity of 44.2M bytes in total is required.
In addition, in a case where images are recorded by using image data transferred from a host computer, the host computer must also handle a huge amount of image data, so that a situation disadvantageously arises in that a major portion of the storage area of a storage device is occupied by the image data, or a high load is applied to the host computer to transfer the image data. With respect to binary image data such as characters and graphic figures, it is possible to overcome the above-mentioned problem by compressing the amount of data through compression processing by converting such binary image data to vector data. With respect to the raster data of a large number of gradations inputted through a scanner or the like, however, it is impossible to effectively compress the image data according to the present compression technique. In addition, it is also conceivable that a large load is applied to the host computer and the printer for compressing and restoring the image data.